1. Field of the Invention
This invention relates to reefing systems for parachutes. In the use of large parachutes, reefing lines are used to restrict the inflow of air into a parachute canopy for a specified time by choking the suspension lines near their connection to the canopy to allow for uniform filling of the canopy. After a specified time period, a pyrotechnic device cuts the reefing line, and the canopy then fills to its full extent.
Reefing line stress on large parachutes (larger than 100 feet diameter) can cause reefing line failures in a large percentage of cases. Characteristically, failure occurs at the point where the reefing line is tied-off in a knot because the line is weakest at this point. Such failures cause premature canopy openings which usually result in canopy failure and always result in poor system performance.
2. Summary of the Prior Art
Pyrotechnically actuated reefing line cutters are known in the art such as the one described in U.S. Pat. No. 3,408,026. The cutter is actuated by firing a charge of pyrotechnic material when the load is dropped from the plane. This charge will ignite a pyrotechnic fuse-like line which will burn for a predetermined time before igniting an explosive compound. The resulting explosion will create pressure for driving the cutting blade forward against the reefing line, thereby severing the line and allowing the parachute to open to a full extent.
An alternative method for actuating reefing line cutters is by altitude-sensitive devices which contain miniaturized radar sensors. At a predetermined altitude, the sensors trigger a charge to actuate cutting of the reefing line.